Substantially amorphous polyolefins useful as pressure-sensitive adhesives

ABSTRACT

The invention relates to a process for the treatment of substantially amorphous polyolefins to provide permanently tacky, low viscosity materials which have useful pressure-sensitive adhesive properties. These permanently tacky amorphous polyolefin homo- and copolymers, as well as blends of such amorphous polyolefins with crystalline polyolefins containing up to 20 weight percent crystalline polyolefin, are novel pressure-sensitive adhesives.

This is a division of application Ser. No. 828,575 filed Aug. 29, 1977,now U.S. Pat. No. 4,143,858.

This invention relates to acid catalyst treated substantially amorphouspolyolefin compositions having a novel combination of properties. Morespecifically, the invention relates to acid catalyst treatedsubstantially amorphous polyolefins which provide pressure-sensitiveadhesive compositions having permanent tackiness.

Pressure-sensitive adhesive (PSA) products have experienced a rapidgrowth rate in recent years because of their ease of application.Typical pressure-sensitive adhesive applications include, for example,tapes (consumer, industrial, and surgical), labels, decals, films, floortile and wall and shelf coverings. Until recently, virtually allpressuresensitive compositions were based on blends of high molecularweight synthetic and natural rubbers with tackifiers. Frequently,fillers such as zinc oxide or magnesium oxide are used in PSAformulations which are applied to opaque backing substrates. Typicalbacking materials include paper, cellophane, plasticized poly(vinylchloride), polyester film, cellulose acetate film, cloth, foamedpolymers (e.g., foamed polystyrene or polypropylene), metal foils, felt,cork and the like. Although PSA compositions have generally been appliedto the backings from solvents, there is a need for PSA materials whichcan be applied as hot-melts to eliminate solvent pollution duringmanufacturing of the products. Also, a non-solvent adhesive is desirablesince many solvents are in short supply.

In polymerization processes for polymerizing propylene using a widevariety of catalysts, some product is formed which is hexane solublewhich has been defined as amorphous polypropylene. This material,however, may contain small fractions which are crystalline. Thisamorphous polypropylene, when solidified from the melt, is initiallytacky and has some pressure-sensitive tack. However, on standing itloses this surface tackiness, due to crystallization of thecrystallizable fraction. These materials for the purposes of thisinvention are defined as substantially amorphous polyolefins.

Substantially amorphous polypropylene provides a good hot-melt adhesivewhen used alone or blended with other materials. These substantiallyamorphous polyolefins are also useful in the lamination ofpaper-to-paper, paper-to-foil and the like when used as a hot-meltadhesive. These substantially amorphous polyolefins, however, are notuseful as pressure-sensitive adhesives as they lose their tackinessafter solidification. For example, substantially amorphous polypropylenebegins to lose its surface tack within six minutes after solidifyingfrom the melt due to crystallization of a polymer fraction. After aboutthree hours the substantially amorphous polypropylene has becomevirtually nontacky. Therefore, it would be an advance in the state ofthe art to provide a permanently tacky substantially amorphouspolyolefin which can be used as a pressure-sensitive adhesive.

Accordingly, it is one of the objects of this invention to provide anovel pressure-sensitive adhesive.

Another and further object of this invention is to provide apressure-sensitive adhesive having good adhesive properties which can beapplied without the use of a solvent.

A still further object of the invention is to provide an adhesiveprepared from a substantially amorphous polyolefin composition which istacky at ambient temperatures.

Another and still further object of this invention is a process forpreparing the permanently tacky amorphous polyolefin compositions usefulas pressure-sensitive adhesives.

A still further object of the invention is the use of these permanentlytacky amorphous polyolefins as pressure-sensitive adhesives.

In accordance with the present invention we have found that asubstantially amorphous polyolefin, such as amorphous polypropylene, canbe treated with an acid catalyst at 250° C. or higher to provide a lowviscosity, permanently tacky, hot-melt pressure-sensitive adhesivecomposition. This treatment renders the substantially amorphouspolyolefin permanently tacky. Substantially amorphous polyolefins usefulin the practice of this invention include substantially amorphoushomopolymers of 1-olefins containing 3 to 5 carbon atoms, substantiallyamorphous copolymers prepared from ethylene and 1-olefins containing 3to 5 carbon atoms, and substantially amorphous propylene or1-butene/higher 1-olefin copolymers containing less than 40 mole percentof at least one higher 1-olefin of the group 1-hexene, 1-heptene,1-octene, 1-nonene, and 1-decene. In defining these polymericcompositions it should be noted that the term "amorphous" as used hereindefines a polymeric composition that may contain a small amount ofcrystallizable portion. Also, these substantially amorphous polyolefinscan be used as a blend with crystalline polyolefins. The crystallizablepolymer component of these blends, however, should not exceed about 20%crystalline polymer.

The melt viscosity of the substantially amorphous polyolefin materialsis generally in the range of about 100 to 200,000 cp. at 190° C. whilethe treated products of this invention generally have melt viscositiesof about 30 to about 50,000 cp. at 190° C. (determined by ASTM D1238).Thus, the acid catalyst treatment causes a decrease in the meltviscosity of the substantially amorphous polyolefin and this treatmentalso imparts permanent tack to the amorphous polyolefin composition.

The properties of amorphous polypropylene are changed significantly bytreatment with acid catalyst. Such catalysts include the strong Lewisacid type catalysts such as aluminum halides, i.e., aluminumtrichloride, antimony halides, i.e., antimony dichloride, boron halides,i.e., boron trifluoride, titanium halides, i.e., titanium trichloride,and silica-aluminum type catalyst such as Davison grade 979silica-alumina catalyst. In particular, it becomes permanently pressuresensitive, less regular, and less opaque; has a lower glass transitiontemperature (Tg); and contains no vinyl or vinylidene unsaturation. Itshould be noted that even the higher viscosity amorphous polypropylenecan be made pressure sensitive by this procedure.

The temperature used in treating the amorphous polyolefins is notcritical. For example, temperatures of 250° C. up to 325° C. aregenerally employed and provide satisfactory results in 2 to 3 hours.However, a higher temperature can be employed and provides similarresults.

One substantially amorphous polyolefin useful in this invention is theessentially noncrystalline hexane soluble polyolefins, such as thesubstantially amorphous polypropylene, formed in minor amounts duringthe production of crystalline polypropylene by the polymerization ofpropylene in the presence of stereospecific catalysts by a process asdisclosed in U.S. Pat. No. 3,679,775, incorporated herein by reference.The solid substantially amorphous polypropylene has a viscosity of about1,000 to about 50,000 centipoise at 190° C. (ASTM D-1238), andpreferably from about 1,500 to about 15,000 centipoise. Thesubstantially amorphous polyolefin can be blended with crystalline,hexane insoluble polyolefin in an amount of up to about 20 percent byweight. One such commercially available amorphous polyolefin useful inpreparing the pressure-sensitive adhesives is Eastobond M-5 polyolefinavailable from Eastman Chemical Products, Inc. These substantiallyamorphous polymers can also be produced directly, i.e., withoutproduction of substantial amounts of crystalline copolymer bypolymerizing a mixture of propylene and butene-1 in mineral spirits at atemperature of about 100° C. to about 180° C. and a pressure in therange of about atmospheric to about 2,000 psig. with the catalystcontaining an organopolylithium aluminum compound and the HA or AA formsof titanium trichloride in a mole ratio of 0.01-0.05/0.1-1.0/1 by apolymerization process as disclosed in U.S. Pat. No. 3,679,775, whichdisclosure is incorporated herein by reference. Methods of preparationof the organopolylithium aluminum compounds are also disclosed in U.S.Pat. No. 3,679,775. These amorphous propylene-1-butene copolymersgenerally contain from about 30 percent to about 75 weight percent ofbutene-1, and have a melt viscosity of about 100 to 100,000 centipoiseat 190° C., a solubility in refluxing hexane of at least 99 weightpercent, a solubility in refluxing diethyl ether of at least 60 weightpercent, a ring and ball softening point in the range of about 78 to120° C., and a differential scanning calorimeter melting point notgreater than 120° C. The substantially amorphous polyolefin could bedegraded to the desired melt viscosity if one starts with a highmolecular weight substantially amorphous polymer.

Suitable reaction vessels include those made from glass or metal. Forexample, the reactions may be conducted in glass flasks, glass linedreactors, steel autoclaves, and the like. The reactions may be conductedin the presence of air or under inert gases such as nitrogen. Althoughnot required, it is also possible to carry out the acid catalysttreatment in the presence of an inert solvent such as heptane.

The pressure-sensitive adhesives of this invention may be stabilized bythe addition of conventional stabilizers for polyolefin materials suchas dilauryl thiodipropionate, Plastanox 1212 (lauryl stearylthiodipropionate), Irganox 1010 {pentaerythritoltetrakis[3(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]}, EastmanInhibitor DOPC (dioctadecyl p-cresol), Plastanox 2246 [2,2'-methylenebis(4-methyl-6-tert-butylphenol)], and Ethyl 702 [4,4'-methylenebis(2,6-di-tet-butylphenol)], or combinations of such stabilizers.Effective stabilizer concentrations may range from about 0.1 to about0.5% by weight. For example, 0.25% Irganox 1010 or a combination of0.25% Irganox 1010 with 0.25% Plastanox 1212 provides good meltviscosity and color stability when the adhesive is maintained in moltenform at 350° F. for 8 hours or longer.

The adhesives of the invention may be used alone or in mixture withother materials, such as polyethylene waxes, polypropylene waxes,amorphous polypropylene, amorphous block ethylene/propylene copolymer,paraffin, polyterpenes such as those commercially available and sold as"Nirez 1100", "Piccolyte S10", "Piccolyte 40", "Piccolyte 100", or"Piccolyte 135"; hydrocarbon resins such as "Piccopale 85", "Piccopale100", "Staybelite", or DAC-B hydrocarbon resin, rubber components suchas ethylene/propylene copolymers, styrene/butadiene (or isoprene) blockcopolymers, and styrene/butadiene copolymers and the like.

Small amounts of pigments, colorants, and other additives may be addedto the treated polyolefins as desired.

The invention can be further illustrated by the following examplesalthough it will be understood that these examples are included merelyfor purposes of illustration and are not intended to limit the scope ofthe invention.

EXAMPLE 1

About 200 grams of low viscosity substantially amorphous polypropylene(melt viscosity 1,800 cp. at 190° C.) is charged to a 500 ml. resinflask. The flask is equipped with mechanical stirrer, nitrogen inlet,and temperature probe. The polymer is heated under a nitrogen blanket to250° C. and is treated with 2 percent of Davison grade 979silica-alumina catalyst while being stirred. After 3 hours, 0.4 percentof Irganox 1010 antioxidant was added, the reaction mixture cooled to200° C., and the treated amorphous polypropylene filtered through aheated funnel. The results obtained are shown in Table I, whichcontrasts amorphous polypropylene, amorphous polypropylene treated at250° C. with 2 percent of the silica-alumina catalyst for 3 hours, andan amorphous polypropylene thermally degraded without catalyst at 250°C. for 3 hours.

                                      Table I                                     __________________________________________________________________________    Comparison of Properties of Amorphous Polypropylene, Silica-Alumina           Treated                                                                       Amorphous Polypropylene, and Thermally Degraded Amorphous Polypropylene       Property    Test Method                                                                            Run 1   Run 2  Run 3 Conclusions                         __________________________________________________________________________    Viscosity at 190° C., cp.                                                          Brookfield Melt                                                                        1,375   1,325  1,800                                                  Viscosity                                                        Softening point                                                                           Ring and ball                                                                           93° C.                                                                         105° C.                                                                       105° C.                           Tg          DSC      -25° C.                                                                        -18° C.                                                                       -16° C.                                                                      Tg lowered 9° C. by                                                    Si-Al                               Regularity  C.sup.13 NMR                                                                           Fewer Isotatic                                                                         --     --   Run 1 less regular than                                   triads than          amorphous polypropylene                                  amorphous            and Run 2                                                polypropylene                                                                 and Run 2                                               Unsaturation                                                                              IR       <0.02% vinyl                                                                          0.37% vinyl                                                                          0.36% vinyl                                                                         Saturation migrates internally                           <0.02%  0.09%  0.18%  during Si-A treatment                                    vinylidene                                                                            vinylidene                                                                           vinylidene                                           Br.sub.2 0.39% total                                                                           0.45% total                                                                          --                                                             unsaturation                                                                          unsaturation                                     Tack        Probe Tack                                                                             150 g.  0 g.   Not tacky to                                                                        Si-Al imparts tack                                                      touch                                     __________________________________________________________________________     Run 1: amorphous polypropylene was treated for 3 hours at 250° C.      with 2 weight percent Davison Grade 979 silicaalumina catalyst.               Run 2: amorphous polypropylene was heated for 3 hours at 250° C.       Run 3: amorphous polypropylene (untreated)                               

EXAMPLE 2

About 200 grams of low viscosity substantially amorphous polypropylene(melt viscosity 1,800 cp. at 190° C.) is charged to a 500 ml. resinflask. The flask is equipped with mechanical stirrer, nitrogen inlet,and temperature probe. The polymer is heated under a nitrogen blanket tothe desired temperature and is treated with the indicated amount ofDavison grade 979 silica-alumina catalyst while being stirred. After thespecified time, 0.4 percent Irganox 1010 antioxidant was added, thereaction mixture cooled to 200° C., and filtered through a heatedfunnel. The results obtained are shown in Table II which summarizes theexperimental results. It is noted that at 200° C. even 2 percentcatalyst does not produce a pressure-sensitive product, and at 250° C.at least 1 percent silica-alumina catalyst is necessary.

                  Table II                                                        ______________________________________                                        Treatment of Amorphous Polypropylene with Silica-                             Alumina Catalyst                                                                     Weight     Tempera-                                                           Si-Al      ture, °C.;                                                                        Viscosity at                                     Run    Catalyst   Time, Hr.  190° C., cp.                                                                    Tacky                                   ______________________________________                                        1      2          200; 3     1,175    No                                      2      2          250; 3     1,375    Yes                                     3      2          250; 4       900    Yes                                     4      1          250; 3     1,400    Yes                                     5      0.5        250; 3     1,550    No                                      6      0.1        250; 3     1,500    No                                      7      2          300; 3       800    Yes                                     8      10         350; 3       425    Yes                                     9      2          250; 3     1,475    Yes                                     10     -- (untreated) -- 1,800      No                                        11     -- (untreated) -- 2,800      No                                        ______________________________________                                    

EXAMPLE 3

About 200 grams of low viscosity amorphous polypropylene treated withcertain Lewis acids also produces permanently pressure-sensitivematerials. In general the viscosities of these materials are lower thanthose produced by treatment with silica-alumina catalyst. Theexperimental results are summarized in Table III. This data shows that(1) at 250° C. at least 0.075 percent AlCl₃ is necessary to produce apressure-sensitive product; (2) at 200° C. 0.075 percent AlCl₃ reducesthe viscosity greatly but the product is not pressure sensitive; (3)other aluminum halides such as AlBr₃ are catalysts; and (4) weak Lewisacids such as hydrated ZnCl₂ are not catalysts for the transformations.

                  Table III                                                       ______________________________________                                        Treatment of Amorphous Polypropylene with Lewis Acids                              Catalyst   Temperature, °C.;                                                                    Viscosity at                                    Run  Weight %   Time, Hr.     190° C., cp.                                                                    Tacky                                  ______________________________________                                        1    AlCl.sub.3, 0.01                                                                         250; 3        1,675    No                                     2    AlCl.sub.3, 0.05                                                                         250; 3        1,500    No                                     3    AlCl.sub.3, 0.075                                                                        250; 3        500      Yes                                    4    AlCl.sub.3, 0.075                                                                        200; 3        575      No                                     5    AlCl.sub.3, 0.1                                                                          250; 3        700      Yes                                    6    AlCl.sub.3, 0.1                                                                            250; 0.5    750      Yes                                    7    AlBr.sub.3, 1                                                                            220; 2        251      Yes                                    8    ZnCl.sub.2, 0.1                                                                          250; 3        1,550    No                                     9    ZnCl.sub.2, 2                                                                            300; 3        1,150    No                                     ______________________________________                                    

The modified amorphous polyolefins of this invention are useful inpressure-sensitive adhesives. As pressure-sensitive adhesives they findutility in preparing tapes by applying the adhesive to conventional hotmelt procedures to a substrate such as a film which can be prepared fromconventional film materials such as a polyester, for example. Thepressure-sensitive adhesive can also be applied onto labels, decals,floor tile as well as wall coverings, such as wallpaper, and shelfcoverings, such as shelf paper.

Although the invention has been described in considerable detail withparticular reference to certain preferred embodiments thereof,variations and modifications can be effected within the spirit and scopeof the invention.

We claim:
 1. A process for preparing tacky modified amorphous polyolefincompositions useful as pressure-sensitive adhesives which comprisesreacting substantially amorphous polyolefin having a melt viscosity ofabout 100 to 200,000 cp. at 190° C. with at least 1 weight percent ofsilica-alumina catalyst at a temperature of at least 250° C. to providea low viscosity, permanently tacky hot-melt pressure-sensitive adhesive.2. A process according to claim 1 wherein said substantially amorphouspolyolefin is a member of the group selected from substantiallyamorphous homopolymers of 1-olefins containing 3 to 5 carbon atoms,substantially amorphous copolymers prepared from either ethylene and1-olefins containing 3 to 5 carbon atoms or propylene and 1-butene, andamorphous propylene or 1-butene/higher 1-olefin copolymers containingless than 40 mole percent of at least one higher 1-olefin of the groupconsisting essentially of 1-hexene, 1-heptene, 1-octene, 1-nonene, and1-decene.